U.S. patent application number 14/238901 was filed with the patent office on 2015-02-19 for curing system.
This patent application is currently assigned to INTRINSIQ MATERIALS LTD.. The applicant listed for this patent is Richard Dixon, Daniel Johnson, Jose Pedrosa. Invention is credited to Richard Dixon, Daniel Johnson, Jose Pedrosa.
Application Number | 20150048075 14/238901 |
Document ID | / |
Family ID | 44764526 |
Filed Date | 2015-02-19 |
United States Patent
Application |
20150048075 |
Kind Code |
A1 |
Pedrosa; Jose ; et
al. |
February 19, 2015 |
Curing System
Abstract
Apparatus for curing of nanoparticle material, the apparatus
comprising: a receptacle for receiving a substrate upon which a
laser of the nanoparticle ink has been placed; and a laser bar
diode array comprising a first bar diode laser, the array
configured to emit a laser as a continuous wave and to cure the
deposited nanoparticle material.
Inventors: |
Pedrosa; Jose; (Farnborough,
GB) ; Johnson; Daniel; (Farnborough, GB) ;
Dixon; Richard; (Farnborough, GB) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
Pedrosa; Jose
Johnson; Daniel
Dixon; Richard |
Farnborough
Farnborough
Farnborough |
|
GB
GB
GB |
|
|
Assignee: |
INTRINSIQ MATERIALS LTD.
Farnborough, Hampshire
GB
|
Family ID: |
44764526 |
Appl. No.: |
14/238901 |
Filed: |
August 16, 2012 |
PCT Filed: |
August 16, 2012 |
PCT NO: |
PCT/GB2012/052002 |
371 Date: |
November 3, 2014 |
Current U.S.
Class: |
219/410 |
Current CPC
Class: |
H05B 1/023 20130101;
B05D 3/067 20130101; B05D 3/0209 20130101; B05D 3/06 20130101 |
Class at
Publication: |
219/410 |
International
Class: |
H05B 1/02 20060101
H05B001/02 |
Foreign Application Data
Date |
Code |
Application Number |
Aug 16, 2011 |
GB |
1114048.0 |
Claims
1. An apparatus for curing of nanoparticle material, the apparatus
comprising: a receptacle for receiving a substrate upon which a
layer of the nanoparticle material has been deposited, the
nanoparticle material comprising a nanoparticle ink or paste; and a
laser bar diode array comprising a first diode bar laser, the array
configured to emit a laser beam as a steady state wave which cures
the deposited layer of nanoparticle material.
2. An apparatus of claim 1, wherein the laser beam extends the
width of the deposited layer of the nanoparticle material.
3. An apparatus of claim 1, wherein the apparatus further comprises
an optical array placeable between the laser bar diode array and
the substrate and configured to modify the wavefront emitted by the
laser bar diode array.
4. An apparatus of claim 3, wherein the optical array is configured
to focus or diffuse the emitted laser beam.
5. An apparatus of claim 3, wherein the optical array comprises a
first aperture configured to produce a "top-hat" type
wavefront.
6. An apparatus of claim 3, wherein the optical array comprises a
first lens.
7. An apparatus of claim 1, further comprising one or more further
diode bar lasers.
8. An apparatus of claim 7, wherein the plurality of diode bar
lasers are placed in series.
9. An apparatus of claim 7, wherein two or more of the diode bar
lasers are configured to emit at different frequencies.
10. An apparatus of claim 9, wherein a second diode bar laser is
configured to dry or "soft" sinter the deposited material.
11. An apparatus of claim 1, further comprising a processor
configured to control the apparatus.
12. An apparatus of claim 11, wherein the processor is part of a
controller unit configured to selectively engage the one or more
diode bar lasers.
13. An apparatus of claim 11, wherein the processor is configured
to control the intensity of the emitted laser beam.
14. An apparatus of claim 12, wherein the controller unit further
controls the current supplied to the laser bar diode array.
15. An apparatus of claim 11, further comprising a sensor
configured to measure the temperature of the apparatus.
16. An apparatus of claim 15, wherein the sensor is in
communication with the processor and the processor is further
configured to maintain the temperature below a predetermined value
by selectively adjusting the intensity of the laser beam.
17. An apparatus of claim 1, further comprising a computer
configured to receive information regarding the deposited layer of
the nanoparticle material and/or substrate.
18. An apparatus of claim 17, wherein the computer is further
configured to determine the relative separation between the
receptacle, optical array, and laser bar diode array based on the
received information.
19. An apparatus of claim 1, further comprising a heat sink.
20. An apparatus of claim 1, wherein the receptacle and laser bar
diode array are moveable relative to each other.
21. An apparatus of claim 1, wherein the laser bar diode array is
configured to emit at a frequency which is transparent to the
substrate.
22. An apparatus of claim 1, further comprising a source of inert
gas to provide an inert atmosphere in which the nanoparticles are
cured.
23. An apparatus of claim 1, further comprising one or more further
laser bar diode arrays.
24. An apparatus of claim 1, further comprising a chamber in which
the receptacle is placed and configured to reduce reflections of
the laser light.
25. An apparatus of claim 1, wherein the wavelength emitted by the
laser bar diode is such that the substrate is transparent.
26. An apparatus of claim 1, further comprising a heating element
for heating the substrate.
27. An apparatus of claim 1, wherein the receptacle is a vacuum
bed.
28. An apparatus of claim 27, wherein the vacuum bed is water
cooled.
29. An apparatus of claim 7, wherein a first laser is configured to
emit at a lower power than a second laser, the first laser thereby
soft sintering the deposited layer of nanoparticle material.
30. An apparatus of claim 1, wherein the steady state laser is a
continuous or quasi-continuous laser.
Description
TECHNICAL FIELD
[0001] The present invention relates to apparatus for curing
nanoparticles. In particular to a system which uses diode bar
lasers to cure nanoparticles.
BACKGROUND TO THE INVENTION
[0002] It is known to cure or sinter nanoparticles to produce large
scale structures from nanoparticles. An advantage of curing
nanoparticles is that the temperatures involved for curing
nanoparticles is significantly lower than for the bulk curing of
larger particles of the same material.
[0003] Known, commercially available, systems for curing
nanoparticles typically involve the use of convection ovens or
Xenon flash lamp based systems. In such systems the Xenon lamps
emit pulsed light which is directed onto films of nanoparticles to
be cured. The light emitted by the lamps is of sufficient energy to
cure the nanoparticles.
[0004] Such prior art systems however suffer from a number of
deficiencies. For example, due to the natural spread in wavelengths
of the emitted light source from the Xenon lamp, contributions from
non-peak energy wavelengths can result in unwanted effects. For
example, the spread in wavelength may result in limited penetration
of the light into thicker films or sealing top surface layers
trapping unwanted organic species in the remaining structure. This
occurs because light from the higher frequency, and therefore
higher energy, from the tail of the energy distribution is readily
absorbed in the near surface region sintering this region.
Accordingly, the binder or organic suspension in which
nanoparticles are typically held is only partially removed,
limiting the conductivity. The non-symmetrical distribution of
intensity of energy also produces energy which is not used in the
process of sintering and accordingly reduces the efficiency of the
curing. This can also heat and damage the substrate used.
[0005] The pulsing effect of the lamp, or indeed other light
sources, furthermore tends to create high energy peaks which are
found to ablate films rather than cause the sintering process.
Accordingly, the structure of the cured product may not have the
desired structure.
[0006] The prior art also suffers from limitations on the number of
substrates that can be used, particularly high thermal conductivity
materials such as aluminium, silicon and ceramics, as the heat is
conducted away from the area of incident light before sintering can
take place. High thermal mass materials are routinely used in
applications such as LED systems as part of efficient heat sink
systems. Furthermore, some of the wavelengths of the lamps are
known to cause damage to certain substrates, due to these
wavelengths of light being readily absorbed by the substrate and
causing heat damage. This is known to occur with polymeric and ITO
films, and therefore affects the suitability of the curing method
for certain materials.
[0007] To overcome at least some of the problems detailed above
there is provided a curing apparatus which comprises an array of
one or more diode bar lasers, preferably arranged in series, which
emits a continuous or quasi-continuous beam to cure the
nanoparticles. Each diode bar laser contains a one-dimensional
array of broad area emitters, arranged so that the laser beam
emitted, or laser `curtain`, is configured to extend across the
width of a substrate allowing it to cure large surface areas of
material very rapidly.
[0008] In the present specification the size of the particle is
used to refer to the diameter of the particle. The term continuous
wave, as is accepted in the art, refers to a laser beam that is
produced as a continuous output beam i.e., a beam that is not
pulsed. Such beams are steady-state beams and typically have a
constant amplitude and frequency. Quasi-continuous lasers, as is
accepted in the art, refer to laser beams that are pulsed, but
emit--during the emission phase--a laser that has a continuous
output i.e., at a constant amplitude and frequency. Such
quasi-continuous beams are only switched on for a certain time
period, which is long enough for the laser to emit at a steady
state (i.e., constant amplitude and frequency). Therefore, a steady
state beam is taken to refer to lasers which have a constant
amplitude and frequency, such as continuous and quasi-continuous
beams.
[0009] Advantageously the apparatus allows for a high level of
control of the curing diode bar laser which helps maintain the
efficiency in the curing process. It is found that, due to the
uniform nature of the curing beam, the invention also allows for a
better penetration of the material being cured with the array
helping to ensure that lower layers of deposited films of
nanoparticles are cured. Advantageously, as the array uses
monochromatic diode bar lasers, the curing light does not have a
higher energy tail as found in prior art systems to cause many of
the aforementioned problems.
[0010] A further benefit of the invention is that it is found to
remove a higher proportion of organic binder/solvent which is
present in the deposited nanomaterials. As the present invention
allows for a greater control of the light used to cure the
materials, in terms of wavelength/energy and energy distribution,
the curing laser beam used can be adapted to ensure removal of
organic binders/solvents.
[0011] According to an aspect of the invention there is provided
apparatus for curing of nanoparticle material, the apparatus
comprising: a receptacle for receiving a substrate upon which a
layer of the nanoparticle ink has been placed; and a laser array
comprising a first diode bar laser, the array configured to emit a
laser beam as a continuous or quasi-continuous wave and to cure the
deposited nanoparticle material.
[0012] Optionally, wherein the laser extends the width of the
deposited nanoparticle ink layer. Optionally, wherein the apparatus
further comprises an optical array placeable between the laser
array and substrate and configured to modify the wavefront emitted
by the laser array. Preferably, wherein the optical array is
configured to focus or diffuse the emitted laser beam. Preferably,
wherein the optical array comprises a first aperture configured to
produce a uniform wavefront.
[0013] Optionally, wherein the optical array comprises a first
lens. Optionally, further comprising one or more further diode
lasers. Preferably, wherein the plurality of diode lasers are
placed in series. Preferably, wherein two or more of the lasers are
configured to emit at different frequencies. Preferably, wherein a
second laser is configured to dry the deposited material.
Optionally, further comprising a processor configured to control
the apparatus. Preferably, wherein the processor is part of a
controller unit configured to selectively engage the one or more
lasers. Preferably, wherein the processor is configured to control
the intensity of the emitted lasers. Preferably, wherein the
controller further controls the current supplied to the laser
array. Optionally, further comprising a sensor configured to
measure the temperature of the apparatus. Preferably, wherein the
sensor is in communication with the processor and the processor is
further configured to maintain the temperature below a
predetermined value by selectively adjusting the intensity of the
laser. Optionally, further comprising a computer configured to
receive information regarding the deposited material and/or
substrate. Preferably, wherein the computer is further configured
to determine the relative separation between the receptacle,
optical array and laser based on the received information.
[0014] Optionally, wherein the receptacle and laser array are
moveable relative to each other. Optionally, further comprising a
heat sink. The sample holder or receptacle is also required to hold
the substrate flat; this can be achieved via use of a vacuum bed.
The bed can be designed such that it is water cooled to ensure the
substrate is maintained at a constant temperature during processing
so that the sintering is more uniform. Alternatively the substrate
can be heated such that lower laser power is required to complete
the sintering process. Optionally, wherein the laser array is
configured to emit at a frequency which is transparent to the
substrate. Optionally, further comprising a source of inert gas to
provide an inert atmosphere in which the nanoparticles are cured.
This can be done by ensuring the sintering laser chamber contains
an inert or reducing atmosphere or by blowing inert gas such as
argon across the substrate during sintering, this also aids in
removing any organic material from the substrate. Optionally,
further comprising one or more further laser bar diode arrays.
Optionally, further comprising a chamber in which the receptacle is
placed and configured to reduce or use reflections of the laser
light. In the case of reflections the backscattered light may be
used to help sinter the rear side of the substrate, for example
when curing films on PET or other transparent films. Optionally,
wherein the wavelength emitted by the laser diode is such that the
substrate is transparent and no or minimal heating effects are
caused by the direct impact of the laser on the substrate.
[0015] Optionally the apparatus further comprises a heating element
for heating the substrate. Optionally, wherein the receptacle is a
vacuum bed. Preferably wherein the vacuum bed is water cooled.
Optionally in embodiments with multiple lasers wherein a first
laser is configured to emit at a lower power than a second laser,
the first laser thereby soft sintering the deposited nanoparticle
ink.
[0016] Other aspects of the invention will be apparent from the
appended claim set.
BRIEF DESCRIPTION OF THE FIGURES
[0017] Embodiments of the invention are now described, by way of
example only, with reference to the accompanying drawings in
which:
[0018] FIG. 1 is a schematic representation of the apparatus used
according to an aspect of the invention;
[0019] FIGS. 2a and 2b are a schematic representation of the laser
array according to an aspect of the invention;
[0020] FIG. 3 is a schematic representation of a laser array
comprising a plurality of lasers;
[0021] FIG. 4 is a flow chart of the process of curing a material
according to an aspect of the invention; and
[0022] FIG. 5 is plot of a power distribution curve from a laser
bar diode.
DETAILED DESCRIPTION OF AN EMBODIMENT
[0023] According to an aspect of the invention there is provided an
apparatus to cure nanoparticles. In particular for the bulk curing
of nanoparticles. The processes described herein are suitable for
scaling from a worktop implementation to an industrial
implementation.
[0024] FIG. 1 shows a schematic representation of a curing
apparatus 10. There is shown a chamber 12 in which the apparatus is
held. The apparatus 10 comprises a diode bar laser array 14, which
has an optical array 16 through which light from the diode bar
laser array 14 passes onto a holder or receptacle 18, with a heat
sink 20, upon which a substrate 22 is placed. The substrate 22 has
a layer of nanoparticle ink 24 which is to be transformed (by
sintering or curing). The apparatus is controlled by a computer 26
which controls the laser current supply 28 and an optics controller
30, it also receives inputs from a temperature sensor 32.
[0025] In a preferred embodiment the apparatus provides a chamber
12 in which the curing apparatus 10 is placed. The chamber 12 is
coated with a paint which absorbs the light emitted from the laser
array 14 and minimises reflections from the laser array 14. The
chamber 12 also contains the apparatus in an inert atmosphere (i.e.
in an atmosphere with a high concentration of inert gases) or a
reducing atmosphere (i.e. an atmosphere in which oxygen and other
oxidising gases are removed, such as 0-10% hydrogen in argon). The
inert, or reducing, atmosphere advantageously ensures that the
curing process results in the production of a film with minimal or
zero oxide content, thereby increasing the purity of the production
process. In other embodiments, to reduce costs, the chamber 12 may
be omitted.
[0026] The diode bar laser array 14 is placed above receptacle 18
and is positioned so as to emit a laser beam onto the receptacle
18. The optical array 16 is positioned between the laser array 14
and the receptacle 18, so as to selectively vary the intensity of
the emitted waveform by the laser array 14. The laser array 14 is
powered by a current supply 28 which is controlled by a computer
26. The computer 26 is also enabled to select and place the
appropriate optics in the optical array 16.
[0027] In use, the laser emitted by the laser array 14 cures the
nanoparticles by sintering the individual particles so as to form a
larger structure. Additionally, the laser has the effect of
removing many organic compounds associated with the nanomaterial,
thereby making a structure with a high purity. As the curing
preferably occurs in a chamber 12 with an inert, or reducing,
atmosphere, oxidisation of the formed structure is minimised.
[0028] In use, a substrate 22 coated in the nanomaterial 24 to be
cured is placed on the receptacle 18. The substrate 22 is covered
in nanoparticle material 24 via known methods such as printing. The
nanoparticle material 24 may be a metal or semi-metal, such as
copper, silver, silicon, nickel, tantalum, titanium, platinum,
palladium, molybdenum, or aluminium. The nanoparticle material 24
is placed on a substrate 22, which may be a plastic such as
polyimide (PI), polyethylene (PE), polypropylene (PP), Polyethylene
terephthalate (PET), Polyethylene naphthalate (PEN), polycaronate
(PC), or other suitable materials such as silicon nitride (SiN),
Indium tin oxide (ITO), glass, Acrylonitrile butadiene styrene
(ABS), ceramic, FR4, GX13, or paper.
[0029] The substrate 22 is placed on the receptacle 18, such as a
curing table, though any suitable receptacle for holding the
substrate 22 may be used. In the preferred embodiment the
receptacle 18 and the laser array 14 are moveable relative to each
other to allow for greater coverage. In a preferred embodiment the
receptacle 18 is a table which can translate in the x-y plan,
thereby increasing the coverage of the laser array 14. In a further
embodiment the laser array 14 and receptacle 18 are fixed in
relative positions and the beam emitted by the laser array 14 is
controlled by the optical array 16 thereby allowing the beam
emitted by the laser array 14 to cover the entire substrate 22 and
therefore deposited nanomaterial 24.
[0030] The substrate 22 is illuminated by a beam from the diode bar
laser array 14. The diode bar laser array 14 comprises one or more
diode bar lasers. In embodiments with a plurality of diode bar
lasers, the lasers are preferably placed in series. Diode bar
lasers are commercially available and emit a beam which is
essentially one dimensional extending several centimetres in a
first axis (known as the slow axis) and a few millimetres in a
second axis (known as the fast axis). The present invention takes
advantage of the natural shape of the diode bar laser output to
provide a beam that has a highly regular, rectangular shape. The
diode bar lasers emit a continuous or quasi-continuous wave beam,
that is to say a beam of constant amplitude and narrow spectrum.
Thus the laser emits in a steady state. Therefore, unlike in Xenon
systems there is no variation in the amplitude or frequency of the
light source. In a preferred embodiment the laser emits at 808 nm,
915 nm, 938 nm, 975 nm or 976 nm, with a FWHM of <3 nm. However,
other frequencies may be used and indeed depending on the material
to be cured, and the substrate, the wavelength used is preferably
different so as to ensure the optimal penetration and removal of
organic species. Laser bar diodes operating in the range from 600
nm to greater than 2 .mu.m can be used, with the higher laser
wavelengths being suitable for curing thicker deposited layers.
[0031] FIG. 5 shows the typical power distribution of a single
laser bar diode. There is shown the power distribution for two runs
R1 (shown as diamonds) and R2 (shown as squares).
[0032] As is shown in FIG. 5 laser bar diodes exhibit some
non-uniformity due to temperature variations or differences in the
semiconductor diodes across the bar. As shown in FIG. 5 the shape
of the beam is constant across runs R1 and R2 and therefore the
uniformity of the beam may be improved by use of several laser bar
diode arrays positioned such that the emitted light overlaps. As
the shape of each laser beam is known the laser bar diodes are
positioned such that the overall effect is to average the emitted
power and make the laser wavefront more uniform in intensity.
[0033] In embodiments of the invention which use multiple laser bar
diodes in the laser array, the first laser may be operated at lower
power/longer wavelength than one or more of the other laser bar
diodes. The first laser therefore acts to drive off more organic
content, thereby reducing or eliminating drying requirements.
Furthermore, the use of the lower power first laser "soft" sinters
the particles together densifying the structure and reducing
mobility of the particles during the final sintering process stage
(at higher power, with the other lasers). This helps to reduce
effects such as Ostwald ripening where particles are sufficiently
mobile to cause surface balling (lowering the overall surface
energy). Equally the same laser may be used with the substrate
passing multiple times through the laser curtain but with the laser
bar diode bar power adjusted for each pass.
[0034] In other embodiments materials can be processed using
alternative known drying methods, such as IR and UV lamps. Improved
conductivity can be obtained by curing the metal in the `wet` form
which allows for greater mobility of the nanomaterials forming more
dense structures and enabling higher conductivities to be
achieved.
[0035] In a preferred embodiment an optical lens or array 16 is
placed between the laser array 14 and the receptacle 18. The
optical lens 16 is used to focus the beam onto the sample.
Depending on the sample position relative to the focus position,
the beam is of variable height (whilst maintaining a fixed width)
allowing the energy density to be controlled. In an embodiment, a
single lens whose length encompasses the output of the bar diode
(which diverges), or several bar diodes in series, is used. For a
given beam width, the working depth of the beam can be increased
allowing greater tolerance on the substrate position relative to
the laser array 14 by incorporating an additional lens to collimate
the beam. In an embodiment the optical array 16 comprises a
plurality of lenses, apertures, masks and gratings to provide a
high level of control of the emitted laser beam.
[0036] The focussing of the beam is particularly useful for
materials and substrates with high thermal conductivities that
require a higher intensity beam to undergo structural changes via
curing. By focussing the beam, the effective temperature of the
beam can be raised allowing for curing of higher thermal
conductivity material.
[0037] The form and functionality of the optical lens array is
discussed in further detail with reference to FIG. 4.
[0038] In a further embodiment, the laser array 14 comprises a
plurality of diode bar lasers of different wavelengths. As the
interaction between the emitted laser light and a substance
(deposited nanomaterial, substrate, etc) is governed by the energy
of the emitted light photons, in an embodiment of the invention,
there is provided a laser array 14 which comprises a plurality of
diode bar lasers that emit at different wavelengths and therefore
emit light photons of different energies. Depending on the
nanomaterial 24 used and the substrate 22 material upon which the
nanomaterial 24 is placed, the laser(s) selected by the computer 26
are optimally selected to ensure curing of the nanomaterial 24
whilst avoiding damage to the substrate 22 material. Optionally, if
multiple nanomaterials 24 are deposited onto the substrate 22,
and/or multiple substrates 22 are used, multiple lasers can be
emitted by the laser array 14.
[0039] The optical array 16 further allows for the selection of a
number of different lenses or masks depending on the desired
waveform. In particular apertures or masks can be selected to
produce a uniform waveform with a constant energy. The waveform
advantageously enables a very fast transition from the uncured to
cured state or from undried to a dried condition. The invention
advantageously overcomes many of the problems associated with the
broadband wavelength emission of a Xenon lamp. For example, the
present invention uses a monochromatic light source and therefore
eliminates the contribution from other wavelengths such as lower
wavelength light that is heavily absorbed in the upper layers
therefore sealing the upper layers. Advantageously the laser bar
diode used allows for the removal of a greater portion of
materials, such as organic binder, in the precursor nanomaterial.
This is a consequence of the waveform not sealing the upper layers
as in the prior art, therefore allowing the laser to penetrate to a
greater depth.
[0040] A further advantage is the use of steady state or
continuous/quasi-continuous wave lasers as it is found that by
using a continuous wave with a top hat waveform high energy peaks
associated with Xenon lamps are avoided. These peaks in Xenon lamps
are found to cause ablation of the precursor material rather than
sintering, and therefore the pulsing lamps result in a less
efficient transformation of the precursor material than the
monochromatic continuous wave used in the present invention.
Furthermore, it is found that whilst some substrates are not
affected/damaged by the central wavelength of the Xenon lamp, the
high energy peaks may damage the substrate. It is also found that
high thermal conductivity substrates such as aluminium, silicon and
ceramics conduct heat from the area of incident light before
sintering can take place. The present invention advantageously
overcomes these limitations by using the laser array 14 and
modifying the beam with the optical lens or array 16. These
advantages are also observed on processing coated plastic layers
for example, ITO coated plastic substrates. ITO is known to absorb
at certain wavelengths causing structural damage, the use of a
monochromatic light source allow for the selection of laser
wavelength to optimise the sintering of the nanoparticles whilst
limiting or negating any damage to the coating.
[0041] In a preferred embodiment the power supplied by the laser
bar diode array 14 is controlled by the laser current supply 28. By
increasing the Amps supplied to the laser bar diodes the output of
the lasers can be varied. The optical array 16 can also affect the
intensity by focusing/defocusing the beam and the control of the
optical array 16 is performed by the optics controller 30
(described with reference to FIG. 1). In a preferred embodiment
both the laser current supply 28 and optics controller 30 are
controlled by a central computer 26. The central computer 26
communicates with the laser current supply 28 and the optics
controller 30 to selectively engage/disengage the respective
components to modify the emitted beam. In use, the user inputs into
the computer 26, using known input means such as a keyboard, the
substrate 22 material, and the type, width and depth of deposited
nanomaterial 24. The computer 26 has a form of writeable memory, or
is enabled to access a memory, which comprises a look up table so
that the optimal optical configuration and laser power may be
selected. As discussed above, by focusing or defocusing the laser
beam with the optical array 16 a single diode laser can be used for
a number of different materials. From the input the computer 26
also determines the focusing needed for the laser beam, and/or the
numbers of diode lasers required in order to produce a beam which
extends the width of the substrate. To help maintain the efficiency
of the curing process the laser beam preferably extends the width
of the deposited material. The computer 26 therefore provides an
easily automated system as the control of the system is determined
by the input parameters.
[0042] Once the appropriate laser wavelength, beam size and power
have been selected, the computer 26 configures the laser array 14
and optical array 16 appropriately. The highly tunable nature of
the invention, via the ability to use multiple wavelength lasers,
the variations of the voltage and current, and the use of lenses
allows for an elevated level of control. This control is used to
ensure that the material is sintered, as opposed to ablated, and is
found to produce metal or semi-metal structures which are of higher
purity, and with improved conductivity and adhesion when compared
to Xenon lamp systems.
[0043] In further embodiments the receptacle further comprises a
heat sink 20 and one or more temperature sensors 32. The heat sink
allows for the transfer of heat generated by the laser beam(s) to
be transferred away from the nanomaterial 24 and substrate 22. As
some nanomaterials have a high curing temperature regulation and
removal of the excess heat is desirable to prevent overheating
which may adversely affect other features, in particular the
substrate 22.
[0044] As it is preferred that the receptacle 18 hold the substrate
flat, the receptacle is a vacuum bed. Preferably, the bed is water
cooled to ensure the substrate is maintained at a constant
temperature during processing so that the sintering is more
uniform.
[0045] In a further example of the invention the substrate is
heated such that lower laser power is required to complete the
sintering process.
[0046] In order to prevent excess heat build-up the apparatus 10
advantageously further comprises a temperature sensor 32 which is
in communication with the computer 26. The temperature sensor 32
may be a commercially available sensor used in annealing ovens and
curing devices. The sensor 32 is in communication with the computer
26 which monitors the temperature of the apparatus 10. In the
memory of the central computer 26 there is preferably stored
predetermined temperature limits for a given substrate 22 and
nanomaterial 24 combination. If the measured temperature approaches
the predetermined temperature limits the computer 26 reduces the
energy of the laser (through the laser power supply), which
subsequently results in a reduction in the temperature of the
apparatus 10. In certain embodiments, if the temperature exceeds a
critical limit (which is associated with a risk, such as fire) the
computer 26 cuts off the laser current supply 28. Therefore, the
temperature sensors 32 act as a safety measure, as well as a
monitor to ensure optimal curing conditions are maintained. In a
preferred embodiment the temperature sensors 32 are used to ensure
that the apparatus is kept within an operating temperature of
15.degree. C. to 35.degree. C.
[0047] FIGS. 2a and 2b show a schematic representation of the laser
and optical arrays 14 and 16 according to an aspect of the
invention. There is shown the diode bar laser array 14, optical
array 16, receptacle 18, substrate 22, and deposited nanomaterial
24 to be cured.
[0048] FIG. 2a is a plan view of the apparatus and FIG. 2b is a top
view of FIG. 2a.
[0049] In FIG. 2a, the fast axis of a laser beam is shown which
extends of the order of a few millimetres. The laser beam emitted
from the laser array 14 passes to the optical lens 16 whereupon it
is focused. In the embodiment shown, the receptacle 18 is movable,
with the direction of movement shown by the arrow in FIG. 2a.
[0050] As the receptacle 18 moves towards the optical lens 16 the
intensity of the laser beam changes. As shown in FIG. 2a, in order
to obtain a beam of maximum intensity the nanomaterial layer 24 is
placed at the focal point of the laser array 14, and accordingly,
at the position shown in FIG. 2a, the laser beam is at a maximum
intensity on the nanomaterial layer 24.
[0051] There is also shown in FIG. 2a possible positions A, B, and
C of the receptacle 18, represented as dash lines. As the
receptacle 18 progresses from positions A to C, the laser beam is
more disperse, and accordingly the intensity of the laser beam
decreases. Therefore, by the relative movement of the receptacle 18
to the laser array 14 the intensity of the laser beam can be varied
according to the requirements of the invention.
[0052] In further embodiments, the receptacle 18 is stationary and
the optical lens 16 is moved relative to the laser array 14 and
receptacle 18, or both the optical lens 16 and receptacle 18 are
moveable relative to each other. Accordingly, the focal point of
the laser beam through a given lens is variable and the laser
intensity on the sample is therefore variable.
[0053] Of importance when moving the array 14 and receptacle 18 is
the focal depth to ensure the laser curtain is at the appropriate
focus point on the substrate. The apparatus may include a height
sensor (not shown). By sensing the height of the substrate 22
relative to the final lens, automatic adjustments in this height
can be achieved by adjusting the separation between the laser array
14 and receptacle 18 ensuring the same focus is achieved. Therefore
as well as adjusting the intensity of the laser beam emitted by the
array 14, the apparatus is configured to ensure that the
appropriate focus point is emitted onto the substrate 24.
[0054] FIG. 2b shows a plan view of the apparatus shown in FIG. 2a.
The optical path of the laser array 14 shown in FIG. 2b represents
the slow axis of the laser. As shown in FIG. 2b, whilst the
receptacle 18 moves relative to the optical lens 16 the size of the
laser beam in the slow axis remains unchanged and accordingly the
laser beam remains incident upon the entire width of the deposited
nanomaterial layers 24 regardless of the relative position of the
laser array 14 and optical lens 16. Therefore, whilst the intensity
of the laser beam varies whilst the receptacle 18 is moved relative
to the optical lens 16 (as shown in FIG. 2a) the coverage of the
laser beam remains unchanged.
[0055] Advantageously by varying the intensity of the laser light
by changing the relative separation of the receptacle 18, optical
lens 16, and laser array 14, the system becomes much less dependent
on the initial set-up that if the optical lens 16 and receptacle 18
were not moveable relative to the laser array 14. Therefore,
initial set up costs associated with the apparatus are greatly
reduced as the apparatus is less sensitive to the initial
calibration of the apparatus.
[0056] Furthermore, the ability to move the sample or lens, allows
for the curing of 3D shapes, by curing a printed 3D image in a
single step. As the laser scans across the substrate to cure the
deposited material the depth of the deposition changes according to
the 3D feature. By inputting to a central computer that is
configured to control the apparatus (discussed in detail with
reference to FIG. 4) the size, shape and depth of the deposited
material a scanning pattern for the 3D printed shape can be
determined. As the laser array 14 scans across the deposited
material, thereby curing the material, by changing the relative
separations of the optical lens 16 and receptacle 18 as the laser
scans across the sample, changes in the depth of the deposited
material can be accounted for. In an embodiment, the intensity of
the laser beam can be varied as the laser array 14 scans across the
sample, with a higher intensity beam used for thicker depositions
of material. In another embodiment, the system is configured so
that the focal point of the laser beam is always incident on the
top surface of the deposited material and accordingly either the
position focal point is varied as the laser array 14 scans across
the deposited material or the focal point is fixed and the position
of the receptacle 18 changes.
[0057] FIGS. 3a and 3b show various configurations of the diode bar
laser array 14 which can be used according to an aspect of the
invention.
[0058] There is shown the diode bar laser array 14 comprising a
plurality of diode bar lasers 31, 33, 34, and 36. There is also
shown the nanomaterial layer 24, substrate 22 and receptacle 18.
The arrow in FIGS. 3a and 3b represents the direction of movement
of the receptacle 18 relative to the laser array 14.
[0059] In FIG. 3a the laser array 14 is configured in a
"horizontal" multiple laser array arrangement. In such an
arrangement, the laser array 14 comprises a plurality of diode
lasers arranged in series. The arrangement of the laser bar diodes
31, 33, 34, and 36 overlap, thereby providing a laser beam that
extends in the X direction. The total effective beam front is shown
in FIG. 3 as X'. As is shown in FIG. 3a the use of multiple lasers
30 to 36 in the laser bar diode array 14 allow for large scale
coverage of the nanomaterial 24 as deposited on the substrate 22.
In an industrial environment, the laser array 14 therefore can
cover an extended area in the X direction.
[0060] FIG. 3b shows a "vertical" arrangement of the laser array
14. In such an arrangement, the individual laser bar diodes 31, 33,
34, and 36 cover substantially the same area in the X direction and
extends in the Y direction. Such an arrangement can be used to
simultaneously cure several samples at the same time.
[0061] Furthermore, where the receptacle 18 (and therefore sample)
moves in the Y direction the use of multiple different frequency
laser bar diodes provides further configurability to the system.
The first bar diode laser 31 can sinter the material whereas the
subsequent lasers 34 and 36 are used to dry the deposited material.
Therefore, greater control can be given to the laser array 14 and
apparatus 10.
[0062] Advantageously, in such an arrangement described with
respect to FIG. 3 with each laser bar diode array having the same
or differing wavelength lasers and placed adjacent in a process
sequence. The curing process can thus be performed using said
sequence of bar diode arrays at varying power densities, and spaced
in such a way, as to create differing sintering effects to
advantageously cure the coating material in a controlled manner.
For example, a long wavelength bar diode laser array may first be
employed to cure material at depth in a coating. The same partially
cured coating can be exposed to a further second, third, etc.,
laser bar diode at lower wavelengths. The lower wavelengths
selected to preferentially cure the material at a shallower depths.
In further embodiments multiple layers of material with varying
degrees of sintering throughout their depth of a coating could be
imparted using such selective wavelengths such that multiple
interfaces and characteristics may result. Therefore, the present
system provides a much greater level of control in terms of depth
and typing sintering as well as ensuring that the substrate remains
undamaged.
[0063] FIG. 4 shows a flowchart of the process of curing
nanomaterials according to an aspect of the invention.
[0064] There is shown the step of inputting the nanomaterial and
substrate type at step S102: inputting the size of the substrate at
step S104: determining the optical and laser arrays to be used at
step S106: powering the laser at step S108: checking the
temperature at step S110: determining whether the temperature is
within an acceptable limit at step S112: reducing the power
supplied to the laser array at step S114: and ending the process at
step S116.
[0065] At step S102 the user of the invention inputs via an
interface such as a keyboard, the nanomaterial that is to be cured
and the material of the substrate upon which the nanomaterial is
deposited. At step S104 the user also inputs the size of the
substrate. In a preferred embodiment the nanomaterial extends the
width of the substrate. If the deposited material is placed in a 3D
shape, the user inputs the shape and depth of the deposit of
nanomaterial to be cured. Preferably, the user at this stage inputs
the thickness of the deposited nanomaterial. Therefore, at stages
S102 and S104 the user has initialised the invention, and has
identified to the central computer the types of material used and
the thickness of the deposited nanomaterial.
[0066] At step S106, the central computer determines the optimal
laser configuration and optical array configuration to cure the
identified nanomaterial. In particular, the choice of lenses and/or
apertures used in the optical array are determined to ensure the
laser emitted by the laser array covers the entire width of the
deposited material and that the wavelength and intensity of the
laser beam is sufficient to cure the entire depth of the deposited
nanomaterial but not adversely affect the substrate.
[0067] The ability to configure the apparatus at steps S102 and
S104 and for the system to calculate the optimal configurations at
step S106 is particularly beneficial in 3D printing. By enabling
the user to define the shape and depth of the printed material the
laser beam can be configured to allow for the curing of the
material in a single step. In particular the receptacle and/or lens
can be moved according to the thickness of the material in order to
ensure a single stage curing of a 3D printed shape.
[0068] At step S108, the computer determines the optimal laser
strength and powers the lasers. As discussed above, the intensity
of the laser is dependent on the amount of the material deposited
as well as the bulk curing temperature of the materials.
Accordingly, the power of the laser beam selected at step S108 is
chosen so as to optimally cure the deposited nanomaterials both in
terms of the material selected and the amount of material
deposited.
[0069] The incident laser will result in the heating of the
apparatus. In order to ensure that the apparatus functions within a
safe limit, and to further ensure that the apparatus does not
adversely affect the substrates, the temperature of the apparatus
is measured at step S110 and altered if necessary at step S112. The
process described with respect to steps S110, S112 and S114
preferably occurs once a second. The central computer comprises a
database which contains a series of predetermined values which
represent an acceptable temperature limit for a given nanomaterial
and substrate combination. The acceptable limits are based on the
likelihood of damage to the substrate and/or nanomaterial based on
the measured temperature, and also preferably contain a safety
limit which represents the risk of unacceptably high temperature
which may lead to an event such as a fire. The measured temperature
is checked against these predetermined limits at step S110.
[0070] At step S112 the computer determines whether the measured
temperature is within an acceptable limit. If the computer
determines that the measured temperature is indeed acceptable the
process returns to step S110. Accordingly, the process therefore
repeats at one second intervals to ensure that any rapid
temperature rises are identified by the central computer. If the
measured temperature is deemed to be unacceptable or approaching an
unacceptable limit at step S112 the process moves to step S114 to
reduce the measured temperature. At step S114 the central computer
reduces the power supply to the laser current supply thereby
reducing the output intensity of the laser beam. Advantageously, as
the reaction of the nanomaterial from the laser is governed by
quantum effects, a reduction in the intensity of the laser will
still result in the curing of the nanomaterial whilst reducing the
temperature of the apparatus. If the temperature is approaching the
safety limits at step S114, the computer disengages all power
supplied to the laser current supply thereby turning off all curing
lasers.
[0071] At step S116 the process ends, wherein all nanomaterials
have been successful cured. Therefore, the invention provides a
highly tuneable system which can be adjusted according to the
conditions of the system. In particular, the invention can be
configured according to the choice of deposited material and
substrate upon which it is placed. Beneficially, the ability to
adjust the frequency and/or intensity of the laser, emitted at a
steady state as a continuous or quasi-continuous wave ensures that
the entirety of the deposited material is cured and the substrate
is not damaged.
[0072] The method and apparatus described therefore allows for a
high speed curing of nanoparticle inks and pastes. The system is
cost effective and highly scalable allowing for low cost and high
production of cured structures, such as printed electronic
conductive surfaces.
[0073] Advantageously, the use of the laser bar diode array allows
for thick layer penetration. It is found that layers of over 30
microns in depth can be fully cured thereby producing highly
conductive surfaces. Furthermore, the curing times for the thick
deposits are reduced compared to known systems and it is found that
deposited nanoparticle inks and pastes can be cured in timescales
of the order of milliseconds.
[0074] The laser bar diode array is also highly tuneable in terms
of beam width, intensity, and power output. The laser emitted to
cure the deposited nanoparticle material can therefore be selected,
and modified during the curing process, to maximise the efficiency
of the system depending on the substrate chosen and the ink or
paste used. Advantageously, due to the continuous wave nature of
the lasers used the parameters of the lasers used are selected to
minimise substrate heating and prevent damage to the substrate.
* * * * *